Effect of lime and fly ash on swelling percentage and Atterberg limits of sulfate-bearing clay

Lime and fly ash are admixtures used to reduce the swelling of clay. The current study added 3%, 5%, and 7% (wt) of lime to sulfate-bearing clay and found that chemical reactions between the lime and sulfate-bearing clay led to ettringite formation as the lime content increased. This mineral shows good potential for water absorption, which increased the swelling percentage and pressure and the plastic properties of the clay. It was shown that lime is incapable of improving the swelling properties of sulfate-bearing clays. Next, 3%, 5%, and 7% (wt) of fly ash was added to the clay. Fly ash suppressed swelling and decreased the plasticity index of the clay. The optimum content of 3% (wt) fly ash improved the swelling properties of the sulfate-bearing clay. The fly ash was then added to 5% lime-stabilized sulfate-bearing clay. The results showed that the fly ash compensated for the negative effects of the lime, reducing the swelling percentage and pressure and the plasticity index of the lime-stabilized sulfate-bearing clay.